1. Field of the Invention
The present invention relates to a metallic gasket to be disposed between a cylinder head and a cylinder block for sealing adjoining surfaces of the cylinder head and the cylinder block of a Diesel engine, for example. More particularly, this invention relates to a metallic gasket comprising two bead substrates made of an elastic metallic plate with a bead portion formed in an outlined shape along a circumferential edge of a combustion chamber hole and an intermediate metallic plate disposed between the two bead substrates.
2. Prior Art
As to a metallic gasket of this kind, a metallic gasket comprising two bead substrates made of an elastic metallic plate with a bead formed along a circumferential edge of a combustion chamber hole, two intermediate plates disposed between the two bead substrates and a compensating member provided with a spacer member carried between the two intermediate plates at a position of the combustion chamber hole rather than a position where the beads are engaged with each other to compensate for an irregularity in a gap between deck surfaces is disclosed in Japanese Patent Application Laid-Open No. Sho 63-293363. Moreover, a metallic gasket comprising two bead substrates made of an elastic metallic plate with a bead formed along a circumferential edge of a combustion chamber hole and two intermediate plates disposed between the two bead substrate, an edge portion of one intermediate plate being held with an edge portion of the other intermediate plate in the form of a grommet to form a compensating bent portion for forming an almost identical step on both surfaces is disclosed in Japanese Patent Application Laid-Open No. Sho 64-65367.
In the metallic gasket disclosed in Japanese Patent Application Laid-Open No. Sho 63-293363, since the spacer member is carried between two intermediate plates at the position of the combustion chamber hole rather than the position where the beads are opposite to each other, an adjoining surface is increased by one to lower a sealing capacity and the sealing member must be fixed by means of welding, adhesion and the like and thus not only is the cost of processing increased, but also it is difficult to provide an accurate thickness to the compensating member and also this becomes one reason of the lowered sealing capacity.
In addition, in the metallic gasket disclosed in Japanese Patent Application Laid-Open No. Sho 64-65367, the edge portion of one intermediate plate is held with the edge portion of the other intermediate plate in the form of a grommet to form the compensating bent portion for forming the almost identical step on both surfaces; but if the compensating bent portion is disposed between the bead substrates on both sides to be fully compressed between a cylinder head and a cylinder block, the bent stepped portion held in the form of a grommet acts as a shim for the beads and thus an amplitude of a stress to the bead substrates is reduced but a bending stress and an amplitude of the bending stress are generated in the bent portion. Consequently, problems have occurred in that cracks and collapses are generated in the bent portion and thus cracks and collapses are brought about also in the bead plates.